Dienes, metallocene-catalyzed polymerization

Walter Kaminsky and Hansjorg Sinn (Univ. Hamburg) discovered the key beneficial role of moist MAO for a metallocene-catalyzed polymerization of olefins, cyciooiefins, dienes, styrenes, etc. The discovery was followed by numerous patents on the modification/improvements, e.g., L. H. Slaugh and... 

Recently, a metallocene/MAO system has been used for the polymerization of non-conjugated dienes [204, 205]. The cyclopolymerization of 1,5-hexadiene has been catalyzed by Zieger-Natta catalyst systems, but with low activity and incomplete cyclization in the formation 5-membered rings [206]. The cyclopolymerization of 1,5-hexadiene in the presence of ZrMe2Cp2/MAO afforded a polymer (Mw = 2.7 x 107, Mw/Mn = 2.2) whose NMR indicated that almost complete cyclization had taken place. One of the olefin units of 1,5-hexadiene is initially inserted into an M-C bond and then cyclization proceeds by further... 

Most addition polymerizations involve vinyl or diene monomers. The opening of a double bond can be catalyzed in several ways. Free-radical polymerization is the most common method for styrenic monomers, whereas coordination metal catalysis (Zigler-Natta and metallocene catalysis) is important for olefin polymerizations. The specitic reaction mechanism may generate some catalyst residues, but there are no true coproducts. There are no stoichiometry requirements, and equilibrium limitations are usually unimportant so that quite long chains are formed 7iv > 500 is typical of addition polymers. 

Trivalent lanthanocene complexes that are isoelectronic (14e, (P) to cationic group 4 metallocenes are also active for olefin polymerization, although their activity is much less than that of Ti and Zr [28,29]. Mashima et al. have reported monocyclopentadienyl rf-diene complexes of tantalum and niobium that are isoelectronic to group 4 metallocenes. These complexes catalyze ethylene polymerization, albeit with low activity [30]. 

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